What They Are
These are bolt-on kits that take about 20 minutes to install. They have virtually no maintenance, are sealed "closed-loop" from the manufacturer, and are designed to be essentially plug-and-play.
Pros and Cons of a Closed-Loop Cooler
They are not expandable, but provide a relatively easy and inexpensive start to liquid cooling. They also tend to carry extensive manufacturer warranties. These kits are meant for CPU cooling only, and are not able to expand to other components.
These solutions tend to be universally applicable. These systems range from $40 to $200+, plus labor cost.